2.4. Performance vs. preference
Roozenburg and Eekels (1995) have approached performance through the following questions: Which function(s) does the product has to fulfil (cf. requirement specification, criteria objectives)? What are the parameters used to assess the functional characteristics (speed, power, strength, accuracy, capacity, etc.)? Preference refers to the relativistic behavioural response to an object, i.e. the decision to select one option rather than another without considering the costs (Keinonen 1998).
Performance has been the domain of ergonomics, and preferences have been relegated to marketing (Meyer & Seagull 1996). A typical ergonomic evaluation is based on speed, accuracy and safety in completing a task. The selling potential of a product is usually subject to an entirely different set of criteria, commonly applied in marketing research. In these cases, people are asked about their preferences, and the design that most respondents ”like” most is often recommended or adopted for production. Eason (1994) points out that a system is usable to the extent that it is actually used, meaning that no matter how ”good” a system is, it is not usable if it is not used by its proposed users.
Keinonen et al. (1998b) pointed out that design methods should be able to deal with interaction at the behavioural and emotional levels. User trials are normally more related to performance. Usability comprises both preference and performance factors (ISO 9241-11 1998), because subjective satisfaction has a lot in common with preference. Performance and preference methods together have been used successfully in, for example, designing cameras for improved holdability (Caplan 1982).
During the evaluation of alternatives, it is not just the extent to which the product meets the expectations in terms of efficiency and effectiveness that determines user satisfaction, but the other benefits of buying the product also play an important role (Engel et al. 1990 in Kemp & van Gelderen 1996). This is described as the motivation process of consumers (Fig. 8). Kemp and van Gelderen (1996) pointed out that there is a need for an evaluation method that addresses specifically the first impressions and initial use phases, i.e. reveals the hedonic/experiential aspects of product use.
Figure 8. Motivation process of consumers (Kemp & van Gelderen 1996, adapted from Engel et al. 1990).
Traditionally, human factors approaches to design have tended to concentrate on usability – the effectiveness, efficiency and satisfaction with which the users can perform tasks with a product (ISO 9241-11 1998). Recently, however, the idea that products are ‘living objects’ with which people have relationships has begun to gain ground (Jordan 1997), leading to initial research on the issue of pleasure. Jordan (1997) defines “pleasure with products” as “the emotional and hedonic benefits associated with products”. He considers four types of pleasure: (1) physio-pleasure: this is to do with the body – pleasures derived from the sensory organs (related to touching and holding products), (2) socio-pleasure: the enjoyment derived from the company of others (refers to social relations and communication enabled by the product), (3) psycho-pleasure: this is gained from accomplishing a task (achieved when the product assists users in accomplishing tasks), and (4) ideo-pleasure: derived from theoretical entities, such as books, music and art (refers to the values products and their use represent).
Pleasure-of-use measurements have been made at Philips (de Vries et al. 1994). For example, the purpose of a CD system is to provide entertainment, and pleasure hence becomes a goal in itself. The satisfaction it offers is less closely related to effectiveness and efficiency. It is therefore necessary to make pleasure-of-use measurable and to give increasing attention to the pleasure dimension. Elementary technologies for measuring, analysing and estimating impressions have been developed recently in Japan (Osawa 1999). The so-called ”engineering of impression” refers to the intent to utilise ”impressions”, which are subjective feelings that people develop toward various objects for engineering purposes.